Associated with the high integration of semiconductor devices in recent years, the pattern size demanded in the production process is being considerably miniaturized. In an ordinary production process of a fine pattern or a fine impurity distribution, a resist pattern is formed by the photolithography technique, and the resist pattern thus formed is used as a mask. For example, a fine pattern is formed by etching various kinds of thin films on a substrate with the resist pattern thus formed used as a mask, and a fine impurity distribution is formed by ion injection to the substrate with the resist pattern thus formed used as a mask.
Upon forming the fine pattern, the photolithography technique is important. The photolithography technique contains processes of resist coating, exposure and development. Miniaturization of a pattern with the photolithography technique has been achieved mainly by decreasing the exposure wavelength. However, the decrease of the exposure wavelength encounters technical limitation, and the production cost is increased by decreasing the exposure wavelength. Thus, there is limitation in decreasing the exposure wavelength.
Under the circumstances, a method for producing a fine resist pattern beyond the limitation of the photolithography technique by exposure has been proposed (see, for example, JP-A-2000-298356). In the method for producing a resist pattern, a resist pattern having been produced by the photolithography technique is subjected to an additional process, thereby further miniaturizing the resist pattern.
In the technique proposed in JP-A-2000-298356, a first resist layer capable of generating an acid is formed on a semiconductor substrate, and a first resist pattern is formed through exposure and development. A second resist layer capable of undergoing crosslinking reaction with the acid present on the first resist pattern is then formed. A crosslinked layer is then formed with the acid supplied from the first resist pattern at the portion where the second resist layer is in contact with the first resist pattern. Thereafter, the portion of the second resist layer that is not crosslinked is dissolved and removed with water or an aqueous solution of a water-soluble organic solvent, thereby forming a second resist pattern. The process of forming the second resist pattern is performed repeatedly, thereby forming a target resist pattern.
Specifically, upon patterning the first resist layer through exposure, an acid is generated at the portion of the first resist layer that is irradiated with light. Through catalytic reaction of the acid thus generated, the portion of the first resist layer that has the acid present therein becomes soluble in the developer solution. The portion of the first resist layer that has became soluble in the developer solution is removed in the development process, but the first resist layer that is adjacent to that portion has a certain amount of the acid present therein. However, the reaction catalyzed with the acid does not proceed to an extent that the resist layer becomes soluble in the developer solution, and thus the acid remains after the development. Consequently, the remaining portion of the first resist layer adjacent to the portion that has been removed through the development has the acid molecules present therein.
In the technique disclosed in JP-A-2000-298356, the second resist layer capable of undergoing crosslinking reaction in the presence of an acid is formed on the first resist pattern. The acid molecules remaining in the first resist pattern are then diffused into the second resist layer by a method of heating or the like. According to the procedure, the second resist layer that is adjacent to the first resist layer containing the acid molecules present therein is insolubilized through the crosslinking reaction.
In the technique, the portion of the second resist layer that has undergone the crosslinking reaction remains mainly in the side wall of the opening of the first resist pattern, and thereby the size of the opening of the resist pattern may be further decreased.